A217217 Dimension of totally primitive elements of the algebra "Baxter" of order n.

0, 1, 0, 1, 4, 19, 96, 511, 2832, 16215, 95374, 573837, 3520228, 21961119, 139038824, 891817687, 5787091552, 37946582995, 251173847170, 1676831257693, 11282156358500, 76453813499219, 521508969157826, 3578990500062417, 24700214881378152, 171359711873508367

Offset

0,5

References

S. Giraudo, Algebraic and combinatorial structures on pairs of twin binary trees, Journal of Algebra, Volume 360, 15 June 2012, Pages 115-157.

Links

Table of n, a(n) for n=0..25.

S. Giraudo, Algebraic and combinatorial structures on Baxter permutations, DMTCS proc. AO, FPSAC 2011 Rykjavik, (2011) 387-398.

Formula

Giraudo gives a generating function.

Prog

(PARI)
baxter(n) = sum(k=1, n, binomial(n+1, k-1) * binomial(n+1, k) * binomial(n+1, k+1) / (binomial(n+1, 1) * binomial(n+1, 2)));
lista(m) = {u = t + t*O(t^m); b = 1 + sum(n=1, m, baxter(n)*u^n); gfbt = (b-1)/b^2; for (n=0, m, print1(polcoeff(gfbt, n, t), ", ")); }
\\ Michel Marcus, Feb 16 2013

Crossrefs

Cf. A001181.

Sequence in context: A122394 A047781 A089354 * A083315 A301417 A025573

Adjacent sequences: A217214 A217215 A217216 * A217218 A217219 A217220

Keyword

nonn

Author

N. J. A. Sloane, Oct 03 2012

Extensions

More terms from Michel Marcus, Feb 16 2013

Status

approved